Studies with Ca. We have characterized the binding of Ca with both the inside and the outside of the human red cell membrane. There are three binding sites on the outside face, two of which appear to be related to sialic acid. There are three binding sites on the inside face whose characteristics are different from the outside sites; two of these appear to be associated with spectrin. We plan to study the interaction of the inner face Ca with membrane ATPase. We may also study the effect of Ca on K flux in inside out vesicles and possibly use the temperature jump apparatus to measure the kinetics of Ca-membrane binding. Displacement of fluorescent probes from membranes. We have developed a method to study the displacement of the fluorescent probes, ANS and NPN from egg lecithin vesicles by the homologous series of short chain linear amides. We will next study the series of monohydric alcohols and of alkyl halides. When we understand exactly where and how these small solutes interact with the vesicles, we will extend our investigation to human red cells and their ghosts. We will also make similar studies on the membrane anesthetic, chlorpromazine and the polypeptide hormone, vasopressin.